八、在Command中传递参数

7.上面Buttom的Command类就是纯命令，什么参数都不接收，这次的ProvinceChangedCommand类在执行命令的时候，能够传参数！采用泛型的形式，给Action添加泛型参数。

8. 在Visual Studio 2022的解决方案资源管理器中，使用鼠标右键单击“Command”文件夹，在弹出菜单中选择“添加--> 类”，在弹出的“添加新项”对话框中，选择添加 “ProvinceChangedCommand”类，这是一个我们要实现的保存操作指令，然后选择“添加”。ProvinceChangedCommand的具体代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using System.Threading.Tasks;
using System.Windows.Input;

namespace WpfGridDemo.NET7.Command
{
public class ProvinceChangedCommand : ICommand
{
///

/// 命令能否执行 ///

readonly Func _canExecute;
///

/// 命令执行的方法 ///

readonly Action _execute;

    /// <summary>  
    /// 命令的构造函数  
    /// </summary>  
    /// <param name="action">命令需执行的方法</param>  
    /// <param name="canExecute">命令是否可以执行的方法</param>  
    public ProvinceChangedCommand(Action<T> action, Func<bool> canExecute)  
    {  
        \_execute = action;  
        \_canExecute = canExecute;  
    }

    /// <summary>  
    /// 判断命令是否可以执行  
    /// </summary>  
    /// <param name="parameter"></param>  
    /// <returns></returns>  
    public bool CanExecute(Object parameter)  
    {  
        if (\_canExecute == null)  
            return true;  
        return \_canExecute();  
    }

    /// <summary>  
    /// 执行命令  
    /// </summary>  
    /// <param name="parameter"></param>  
    public void Execute(Object parameter)  
    {  
        \_execute((T)parameter);  
    }

    /// <summary>  
    /// 事件追加、移除  
    /// </summary>  
    public event EventHandler CanExecuteChanged  
    {  
        add  
        {  
            if (\_canExecute != null)  
                CommandManager.RequerySuggested += value;  
        }  
        remove  
        {  
            if (\_canExecute != null)  
                CommandManager.RequerySuggested -= value;  
        }  
    }

}

}
void ProviceSelectionChangedExecute(object sender)
{
try
{
if (sender is ComboBox)
{
ComboBox drp=sender as ComboBox;
ProvinceCode=drp.SelectedValue.ToString();
GridDbContext db = new GridDbContext();
var list = db.City.AsTracking().ToList();
List citys = list.Where(x => x.ProvinceCode == ProvinceCode).ToList();
cityList = new ObservableCollection();
if (citys != null)
{
citys.ForEach((t) =>

                    { cityList.Add(t); }  
                    );  
                }

                var cityCodes = from city in citys  
                                select city.Code;  
                List<Area> areas = db.Area.AsTracking().ToList().Where(

x => cityCodes.Contains(x.CityCode)).ToList();

                areaList = new ObservableCollection<Area>();  
                if (areas!=null)  
                {  
                    areas.ForEach((t) =>

                    { areaList.Add(t); }  
                    );  
                }  
            }  
        }  
        catch (Exception ex)  
        {  
            throw ex;  
        }  
    }

结果如图：我们看到了省份下拉框中已经了省份信息。

9.通过绑定依赖属性，实现自动刷新需要实现以下三步：

1.Model继承并实现 INotifyPropertyChanged 接口；

2.数据集合使用ObservableCollection集合；

3.View使用Binding数据对象属性;

如果不行再看看集合在赋值前需要实例化，不然就出不来(必须要同一个源才行)

10. 在Visual Studio 2022中打开MainWindows.xmal文件，并将文件中的代码修改成如下：

            <be:Interaction.Triggers>

                <be:EventTrigger EventName="SelectionChanged">  
                    <be:InvokeCommandAction Command="{Binding ProviceChangedAction}"

CommandParameter="{Binding ElementName=cboProvince}"/>

        </ComboBox>  
    </WrapPanel>

    <DataGrid x:Name="gridArea" Grid.Row="1" ItemsSource="{Binding GridAreaList}"

AutoGenerateColumns="False" HorizontalAlignment="Left" VerticalAlignment="Top"
SelectedItem="{Binding Path=AreaVM,
Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}">

        <DataGrid.Columns>

            <DataGridComboBoxColumn Header="城市" Width="120"

ItemsSource="{Binding Path=DataContext.GridCityList,
RelativeSource={RelativeSource AncestorType={x:Type Window}}}"
x:Name="cboCity" ClipboardContentBinding="{x:Null}"
SelectedValuePath="Code" SelectedValueBinding="{Binding Path=CityCode,
UpdateSourceTrigger=PropertyChanged}"
DisplayMemberPath="Name" SelectedItemBinding="{x:Null}" />

    <WrapPanel Grid.Row="2">  
    <Button  x:Name="btnRefresh"  Height="22" Width="120" Click="btnRefresh\_Click">刷新</Button>

11. 在Visual Studio 2022中打开MainWindowsVM.cs文件，实现下拉框的选择事件的Command命令绑定，将通过Command参数传递过来的省份信息，用于数据查询，同时通知UI界面进行数据刷新。具体如下代码：

using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.DirectoryServices.ActiveDirectory;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Controls;
using System.Windows.Input;
using WpfGridDemo.NET7.Entitys;

namespace WpfGridDemo.NET7.ViewModel
{
public class MainWindowVM: ViewModelBase
{
public MainWindowVM() {
cityList = new ObservableCollection();
areaList = new ObservableCollection();
}
private Area m_Area;
///

/// 县镇区数据 ///

public Area AreaVM
{
get { return m_Area; }
set { m_Area = value; }
}
private string m_Province_Code;
///

/// 省--代码 ///

public string ProvinceCode { get => m_Province_Code; set => m_Province_Code = value; }
private ObservableCollection areaList;

     public ObservableCollection<Area> GridAreaList  
     {  
         get { return areaList; }  
         set  
         {  
            areaList = value;  
             RaisePropertyChanged("GridAreaList");  
         }  
    }  
    private ObservableCollection<City> cityList;

    public ObservableCollection<City> GridCityList  
    {  
        get { return cityList; }  
        set  
        {  
            cityList = value;  
            RaisePropertyChanged("GridCityList");  
        }  
    }

    /// <summary>  
    /// 命令要执行的方法  
    /// </summary>  
    void SaveExecute()  
    {  
        try

        {  
            GridDbContext db = new GridDbContext();  
            var list=db.Area.AsTracking().ToList();  
            Area modifyArea = list.Where(x=>x.Id==AreaVM.Id).FirstOrDefault();  
            if (modifyArea != null)  
            {  
                modifyArea.Name = AreaVM.Name;  
                modifyArea.Updated = DateTime.Now;  
                db.SaveChanges();  
            }

        }  
        catch (Exception ex)  
        {

            throw ex;  
        }  
    }

    /// <summary>  
    /// 命令是否可以执行  
    /// </summary>  
    /// <returns></returns>  
    bool CanSaveExecute()  
    {  
        return false;  
    }

    /// <summary>  
    /// 创建新命令  
    /// </summary>  
    public ICommand ClickSaveAction  
    {  
        get  
        {  
            return new Command.SaveCommand(SaveExecute, CanSaveExecute);  
        }  
    }  
    //combobox  
    /// <summary>  
    /// 命令要执行的方法  
    /// </summary>  
    void ProviceSelectionChangedExecute(object sender)  
    {  
        try

        {  
            if (sender is ComboBox)  
            {  
                ComboBox drp=sender as ComboBox;  
                ProvinceCode=drp.SelectedValue.ToString();  
                GridDbContext db = new GridDbContext();  
                var list = db.City.AsTracking().ToList();

                List<City> citys = list.Where(x => x.ProvinceCode == ProvinceCode).ToList();  
                var cityCodes = from city in citys  
                                select city.Code;  
                List<Area> areas = db.Area.AsTracking().ToList().Where(

x => cityCodes.Contains(x.CityCode)).ToList();
areaList.Clear();
if (areas!=null)
{
areas.ForEach((t) =>

                    { areaList.Add(t); }  
                    );  
                }

                cityList.Clear();  
                if (citys != null)  
                {  
                    citys.ForEach((t) =>

                    { cityList.Add(t); }  
                    );  
                }  
            }  
        }  
        catch (Exception ex)  
        {

            throw ex;  
        }  
    }

    /// <summary>  
    /// 命令是否可以执行  
    /// </summary>  
    /// <returns></returns>  
    bool CanSelectionChangedExecute()  
    {  
        return true;  
    }

    /// <summary>  
    /// 创建新命令  
    /// </summary>  
    public ICommand ProviceChangedAction  
    {

        get  
        {

            return new Command.ProvinceChangedCommand<object>(ProviceSelectionChangedExecute,

CanSelectionChangedExecute);
}
}
}

12.在Visual Studio 2022中按F5键，启动WPF应用程序。然后使用鼠标点击省份下拉框，能够看到，界面中DataGrid中的数据，随着下拉框的变化而随之变化。如下图。

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